Transcript Medical Informatics Biomedical Signal Processing

2nd practice
Medical Informatics
Biomedical Signal Processing
TAMUS, Zoltán Ádám
[email protected]
 Action
potential
 Electroneurogram (ENG)
 Electromyogram (EMG)
 Electrocardiogram (ECG)
 Electroencephalogram (EEG)
 Electrogastrogram (EGG)
 Phonocardiogram (PCG)
 Carotid Pulse (CP)
 Vibromyogram (VMG)
 Vibroarthogram (VAG)
 Basic
component of
bioelectrical
signals
 Caused by the
flow of Na+, K+
and Cl- ions
across the cell
membrane
 Resting
potential:
• In their resting state, the membrane readily
permit the entry of K+ and Cl- ions, but
effectively block the entry of Na+ ions.
• The permeability of membrane for K+ is 50-100
times that for Na+ ions.
• A cell in resting state is said to be polarized.
• The resting potential is in order of -60 to -100 mV
 Depolarization:
• When a cell is excited the membrane changes
•
•
•
•
its characteristics and begins to allow Na+ ions to
enter the cell.
This movement of Na+ ions constitutes an ionic
current, which further reduces the membrane
barrier to Na+ ions.
This leads to an avalanche effect: Na+ ions rush
into the cell.
The inside of the cell becomes positive.
The peak value of action potential is about 20
mV
 Repolarization:
• Membrane depolarization also increases the
permeability of membrane for K+ ions via a
voltage-dependent K+ channels.
• The permeability of membrane for Na+ ions
decrease near the peak of depolarization.
• The efflux of K+ ions from the cell makes the
inside more negative thereby effecting
repolarization back to the resting potential.
• Duration in nerve and muscle cells ~1 ms, in
heart muscle cells 150-300 ms
 All-or-none
phenomenon
 Absolute
refractory period:
1 ms in nerve
cells
 Relative
refractory period:
several ms in
nerve cells
 The
ENG is an electrical signal observed as
a stimulus and the associated nerve action
potential propagate over the length of
nerve.
 ENGs may be recorded using concentric
needle electrodes or Ag-AgCl electrodes at
the surface of the body.
 In order to minimize muscle contraction
strong but short stimulus is applied (100 V
amplitude, 100-300 μs).
 ENGs have amplitudes of the order of 10 μV.
 Wrist
 BElbow
- below
the elbow
 AElbow – above
the elbow
 Typical
values of propagation rate or
nerve conduction velocity are:
• 45-70 m/s in nerve fibres
• 0.2-0.4 m/s in heart muscle
• 0.03-0.05 m/s in time delay fibres between the
atria and ventricles.
 Neural
diseases may cause a decrease in
conduction velocity.
 Motor
units
 Single Motor Unit
Action Potential
(SMUAP)
 Normal
SMUAPs
are usually
biphasic or
triphasic
 3-15 ms in
duration, 100300 μV in
amplitude, 6-30
Hz in frequency
range
 The
10-20 system of electrode placement
for EEG recording.
 The
commonly used terms for EEG
frequency range:
• Delta (0.5-4 Hz): deep sleep
• Theta (4-8 Hz): beginning stages of sleep
• Alpha (8-13 Hz): principal resting rhythm
• Beta (>13 Hz): background activity in tense and
anxious subjects

a: delta, b: theta, c: alpha, d: beta, e: blocking of
alpha rhythm by eye opening, f: marker 50 μV, 1 sec
 The
electrical activity of the stomach
consists of rhythmic waves of depolarization
and repolarization of its constituent smooth
muscle cells.
 The activity originates in the mid-corpus of
the stomach, with intervals of about 20 s in
human.
 Recorded by abdomen electrodes e.g. three
electrodes along the antral axis of stomach
and the common reference electrode
The CP is a pressure signal recorded over the
carotid artery.
 Parts of CP:

• P (percussion wave): ejection of blood from the left
ventricle
• T (tidal wave): reflected pulse from the upper body
• D (dicrotic notch): closure of the aortic valve
• DW (dicrotic wave): reflected pulse from the lower body
 Direct
mechanical manifestation of
contraction of a skeletal muscle.
 Accompanies the EMG
 Recorded by contact microphones or
accelerometers placed on the muscle
surface.
 The VAG
is the vibration signal recorded
from a joint during movement (articulation)
of the joint.
 Normal joint surfaces are smooth and
produce little or no sound.
 Joint affected by osteoarthiritis and other
degenerative diseases may have suffered
cartilage loss and produce grinding sounds.
 The VAG is complex signal and difficult to
analyze.